The present invention concerns an ink-jet recording material with a paper substrate that has a coating on at least one side. The coating contains binder and inorganic pigment.
Ink-jet recording materials, including especially those with a paper substrate, are widely known in the prior art.
Previously known ink-jet recording materials usually have a multilayer coating that consists of at least one ink-receiving layer and at least one protective layer, with the one or more protective layers formed above the one or more ink-receiving layers. An intermediate layer joined with the ink-receiving layer is very often additionally provided directly on the substrate.
The essential components of the previously known ink-receiving layers are inorganic pigments and binders. Especially silicon dioxide and the hydroxides and oxides of aluminum are widely used as pigments, and polyvinyl alcohol is widely used as a binder.
EP 0 806 299 A discloses an ink-jet recording paper with an ink-receiving layer and an upper layer that covers the ink-receiving layer. Whereas the ink-receiving layer does not contain any pigments, the upper layer contains inorganic pigment particles. Aluminum hydroxide of the boehmite type with a pore radius distribution of 10-35 Å or 1 to 3.5 nm is cited as an example of an inorganic pigment. Especially barite-coated or polyolefin-coated papers are used as substrates.
DE 19 952 356 A likewise describes an ink-jet recording paper with a multilayer coating. This paper has an ink-receiving layer with fine inorganic particles and a binder resin as a first layer on at least one side of its substrate. The ink-receiving layer is then coated or impregnated with a coating liquid in the form of a cover layer and then dried. The coating liquid contains at least one specific tetraalkoxytitanium dissolved in an organic solvent. Fine inorganic particles that may be used in the ink-receiving layer include, for example, synthetic amorphous silica, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, aluminum hydroxide, aluminum oxide, and alumina hydrate (pseudoboehmite sol), either individually or in combination. The use of alumina hydrate or colloidal silica as fine inorganic particles is described as preferred, and an alumina hydrate with a pseudoboehmite structure is especially preferred.
EP 0 732 219 A proposes a printing medium in which an ink-receiving layer is provided on a liquid-absorbing paper substrate. The ink-receiving layer is covered by a surface layer. The ink-receiving layer consists of a binder and a cationic substance, while the surface layer consists of ultrafine cationic particles of aluminum oxide or alumina hydrate with a particle diameter in the range of 1-500 nm. A glossiness of 45% or more at an angle of view of 75° is disclosed for the surface layer. Aluminum oxide and alumina hydrate are among a large number of substances specified as inorganic pigments of the ink-receiving layer. Organic particles may also be present. A suitable range of particle sizes is given as 0.1 to 20 μm, which corresponds to 100 to 20,000 nm.
EP 0 803 375 A discloses a recording material, especially for ink-jet printing, whose substrate has a porous recording layer that contains both nonionic or cationic water-insoluble resin particles and alumina hydrate particles, with boehmite with a secondary agglomerated particle size of 100-200 nm being preferred. During the production of the recording layer, it is dried in contact with a smooth surface. The recording layer may additionally be covered with a layer of silicon dioxide to improve scratch resistance.
EP 0 810 101 A discloses a recording material with a porous ink-receiving layer, which can contain both the pure hydroxides of aluminum and pure aluminum oxide, including alumina hydrate with a boehmite structure, with the microcrystals of the alumina hydrate oriented with a specific degree of parallelism. One of the objectives of the invention is to make available a recording material with a high degree of glossiness. Values in the range of 51% to 68% are given as examples.
EP 0 875 394 A discloses the use of alumina hydrate that has been treated with rare-earth salts to produce the recording layer of an ink-jet recording material.
Finally, in a recent proposal aimed at improving the shelf life and increasing the printing speed of ink-jet recording materials, EP 1 512 544 A discloses the addition of polynuclear aluminum hydroxo complexes to nanocrystalline inorganic compounds contained in the recording layer. Pseudoboehmite and silicon dioxide with a maximum particle size of 20 nm are especially preferred as these compounds, and the document specifies that they should have a pore volume≧20 mL/100 g. In addition to the nanocrystalline, nanoporous inorganic compounds, the recording layer can also contain other inorganic compounds that are not nanoporous and nanocrystalline as defined above. In addition to one or more disclosed recording layers, the cited document also provides for auxiliary layers. Suitable substrates include especially polyester foils and—if paper is to be used—preferably barite-coated or polyolefin-coated paper. Uncoated papers of various types can also be used, although no information is given regarding their composition and properties. The only comment that can be made here is that they can have large differences.
The prior-art recording materials are aimed for the most part at the high-price sector with very high surface standards, which can be explained by the fact that there is growing demand for high-quality printing stock for color photo printing due to recent rapid increases in the use of digital photography.
However, there is also growing demand for ink-jet recording materials used in everyday business applications, which means, on the one hand, that it should be possible to produce them less expensively than the aforementioned printing stock for digital photography, and, on the other hand, that they should have a significantly higher quality standard than, for example, the simple copying papers that are still widely used. In particular, for ink-jet recording materials to be successfully used in business applications, it should be possible to print them at very high printing speeds with ink-jet printers, and it should be possible to guarantee not only a long shelf life but also good stability of the ink-jet print image towards environmental influences. In any event, the range of applications encompassed by the “business sector” requires costs that are appropriate for these applications. This requires both quantitative limitation of the raw materials that are used and minimization of the production costs.
The prior-art multiple-step processes for the application of several layers conflict with this objective, as does the use of high-cost materials, which, in addition, often require expensive preparation before they are used in the process.